1. Field of the Invention
This invention relates generally to automotive fuel pumps and, more particularly, to impellers in such pumps.
2. Description of the Prior Art
U.S. Pat. Nos. Lochmann et al 4,209,284, MacManus 3,881,839, and Shultz et al 3,418,991, all assigned to the assignee of this invention, describe submerged fuel pumps wherein electric motor portions of the pumps directly drive one or more open vane regenerative pump impellers. In each of the described pumps, the impellers have circumferential arrays of irregularly spaced, radially extending vanes which operate in well known regenerative fashion when the impellers rotate to pump fuel from an inlet at ambient pressure to a discharge at a higher pressure. In the pumps described in Shultz et al U.S. Pat. No. 3,418,991 and MacManus U.S. Pat. No. 3,881,839, the pump inlet body has one or more vapor discharge holes which intersect a wall of a pumping chamber around the impeller near the roots or radially innermost extremities of the spaces between the impeller vanes. When the impellers rotate, the heavier liquid fuel is centrifuged radially out and the lighter vapors are forced radially in and escape back to the tank through the vapor discharge holes. In the pump described in Lochmann et al U.S. Pat. No. 4,209,284, the impeller is disposed in the pumping chamber with predetermined extra side clearance relative to the chamber side walls. A vapor discharge slot in the pump inlet body at a location substantially radially inboard of the roots of the spaces between the impeller vanes opens into the fuel tank. When the impeller rotates, the vapors are driven radially inward along the sides of the impeller and escape through the discharge slot. With either of the described vapor discharge arrangements, if both the pump inlet port and the vapor discharge holes or slot are simultaneously uncovered when an attempt is made to start the engine, as might occur if there is fuel in the tank but the vehicle is parked on an incline, then the impeller may cause vapor to back-flow through the discharge holes or slot which retards or prevents sufficient vacuum at the pump inlet port to draw in sufficient liquid fuel to prime the pump. An impeller according to this invention operates in the anomalous situation just described to retard vapor back-flow through the vapor discharge opening and thereby enhance the vacuum at the pump inlet port.